1. Field of the Invention
The present invention relates to a lithium ion secondary battery and a method of fabricating the same. More particularly, the present invention relates to a battery structure which can be in any form such as thin type battery.
2.Discription of the Related Art
There is a strong demand for the miniaturization and the reduction of weight of portable electronic apparatus. The accomplishment of this demand drastically depends on the enhancement of the battery properties. To this end, a variety of batteries have been developed, and the improvement of batteries have been under way. These batteries have requirements for high voltage use, large energy density, safety, arbitrariness in shape, etc. Lithium ion secondary batteries can be expected to have the highest voltage and energy density among various kinds of batteries and are still under extensive improvement.
A lithium ion secondary battery comprises as essential constituents a positive electrode, a negative electrode, and an ionically-conducting layer provided interposed between the positive electrode and the negative electrode. In lithium ion secondary batteries which have been put into practical use, as the positive electrode there is used one obtained by applying a positive electrode active material made of a powder of lithium-cobalt oxide or the like to a collector which is then formed into a tablet. As the negative electrode there is used one obtained by applying a negative electrode active material made of a powdered carbon-based material or the like to a collector which is then formed into a tablet. As the ionically-conducting layer there is used a porous film made of a polypropylene or the like impregnated with a nonaqueous electrolytic solution.
The state-of-the-art lithium ion secondary batteries comprise a casing made of a metal or the like. Without any casing, it is difficult to keep the connection of the ionically-conducting layer to the positive and negative electrodes, and the resulting peeling of these components off the connection leads to deterioration of battery properties. However, the foregoing casing adds to the weight of the lithium ion secondary battery, making it difficult to reduce the size and weight of the lithium ion secondary battery. At the same time, the rigidity of the foregoing casing makes it difficult to form the battery into an arbitrary shape.
For the purpose of reducing the weight and thickness of lithium ion secondary batteries, batteries requiring no rigid casing are now under extensive study. In order to accomplish this object, it is necessary that the connection of the positive and negative electrodes to the ionically-conducting layer be kept even under no external force.
As an approach concerning the foregoing requirement, a structure having electrodes formed by adhering active materials with an electronically-conducting polymer, said electrodes being connected to each other with a polymer electrolytic solution, or a structure having electrodes and a separator connected to each other with a liquid adhesive mixture is disclosed in U.S. Pat. No. 5,437,692. Further, a method which comprising the formation of an ionically-conducting layer by a gel electrolytic solution is disclosed in WO95/15,589.
However, the approach disclosed in the above cited U.S. Pat. No. 5,437,692 is disadvantageous in that sufficient adhesive strength cannot be obtained, making it impossible to thoroughly reduce the battery thickness, and the ionic conducting resistivity between the ionically-conducting layer and the electrode is too large to give practically sufficient charge-discharge properties. The approach disclosed in the above cited WO95/15,589 is disadvantageous in that the ionically-conducting layer to be connected is plastic, making it impossible to obtain a sufficient adhesive strength and hence thoroughly reduce the battery thickness.
An object of the present invention is to solve the foregoing problems and provide a thin lithium ion secondary battery excellent in properties such as charge-discharge characteristics by securing the desired adhesive strength and ionic conduction between the ionically-conducting layer and the electrodes at the same time.
A first aspect of the lithium ion secondary battery of the present invention is a battery which comprises a positive electrode, a negative electrode, an electrolyte, and an adhesive resin layer which bonds each of said positive electrode and negative electrode to said electrolyte, wherein said adhesive resin layer contains an ionically-conducting polymer compound incorporated therein.
A second aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein an average molecular weight of said ionically-conducting polymer compound is in a range between 10000 and 1000000.
A third aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said adhesive resin layer contains 20xcx9c90 weight % of ionically-conducting polymer compound.
A fourth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said adhesive resin layer contains 40xcx9c80 weight % of ionically-conducting polymer compound.
A fifth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said adhesive resin layer contains a polyvinylidene fluoride and ionically-conducting polymer compound incorporated therein.
A sixth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said adhesive resin layer contains a polyvinyl alcohol and an ionically-conducting polymer compound incorporated therein.
A seventh aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said electrolyte is constituted by a separator retaining an electrolytic solution.
A eighth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said electrolyte is constituted by a solid electrolyte.
A ninth aspect of the lithium ion secondary battery is a battery according to the eighth aspect of the present invention, wherein said ionically-conducting polymer compound is constituted by a material different from said solid electrolyte.
A tenth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said ionically-conducting polymer compound is one containing one or more ethylene oxide units in the molecular structure.
A eleventh aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least one of a poly(alkylester acrylate) and poly(alkylester methacrylate).
A twelfth aspect of the lithium ion secondary a battery is a battery according to the first aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least one of a poly(hydroxyalcoxyester acrylate), poly(hydroxyalcoxyester acrylate), poly(hydroxyalkylester methacrylate) and poly(hydroxyalcoxyester methacrylate).
Preferably another aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least two compounds selected from the group consisting of the following compounds (1), (2) and (3):
(1) Compound containing one or more ethylene oxide units in the molecular structure:
(2) Poly(alkylester acrylate) or poly(alkylester methacrylate); and
(3) Poly(hydroxyalkylester acrylate), poly(hydroxyalcoxyester acrylate), poly(hydroxyalkylester methacrylate) or poly(hydroxyalcoxyester methacrylate).
A thirteenth aspect of the lithium ion secondary battery is a battery according to the first aspect of the present invention, which comprises a plurality of electrode laminates having a positive electrode and a negative electrode bonded to an electrolyte through an adhesive resin layer containing an ionically-conducting polymer compound incorporated therein.
A fourteenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said plurality of electrode laminates are arranged that said positive and negative electrodes are interposed alternately between plurality of cut electrolytes.
A fifteenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said plurality of electrode laminates are arranged that said positive and negative electrodes are interposed alternately between wound plural electrolytes.
A sixteenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said plurality of electrode laminates are arranged that said positive and negative electrodes are interposed alternately between folded plural electrolytes.
A seventeenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said ionically-conducting polymer compound is one containing one or more ethylene oxide units in the molecular structure.
A eighteenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least one of a poly(alkylester acrylate) and poly(alkylester methacrylate).
A nineteenth aspect of the lithium ion secondary battery is a battery according to the thirteenth aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least one of a poly(hydroxyalkylester acrylate), poly(hydroxyalcoxyester acrylate), poly(hydroxyalkylester methacrylate) and poly(hydroxyalcoxyester methacrylate).
Preferably another aspect of the lithium ion secondary battery is a battery according to the fourteenth aspect of the present invention, wherein said ionically-conducting polymer compound comprises at least two compounds selected from the group consisting of the following compounds (1), (2) and (3):
(1) Compound containing one or more ethylene oxide units in the molecular structure:
(2) Poly(alkylester acrylate) or poly(alkylester methacrylate); and
(3) Poly(hydroxyalkylester acrylate), poly(hydroxyalcoxyester acrylate), poly(hydroxyalkylester methacrylate) or poly(hydroxyalcoxyester methacrylate).
A twentieth aspect of the method of fabricating a lithium ion secondary battery is a method of the present invention, which comprises the steps of:
coating an adhesive resin layer on both surfaces of an electrolyte;
laminating a positive electrode and a negative electrode on the both surfaces of the electrolyte respectively to form a laminate.